The present application is based on French patent application 0000073, filed on Jan. 5, 2000, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to the coupling of pipes made of a composite material comprising reinforcing fibers and thermoplastic.
2. Description of the Related Art
Such pipes, used especially for conveying pressurized fluids, are generally preferred to cast iron or cement pipes because of their much lesser weight, which consequently means that they are easier to handle in the field.
In any installation, it is necessary to ensure continuity of the pipes by use of a sealed coupler able to withstand stresses effectively. Patent Application FR 2,728,051 discloses a coupling device for connecting one end of a composite pipe based on a reinforced thermoplastic to one end of another composite pipe. This device comprises a coupling sleeve and an annular sealing member placed inside the coupling sleeve, the sleeve being provided on its internal wall with a screw thread intended to engage with complementary screw threads in the thickness and on the external surface of the ends of the two tubes to be coupled. According to this device, the screw thread of the coupling sleeve extends over a minimum length which depends on the diameter of the yarns constituting the reinforcing material for the pipes, so as to obtain a pull-out strength greater than the tensile strength of the reinforcing material.
One of the drawbacks of this coupling device relates to the screw thread made in the thickness of the pipes, at their ends. This is because, in the field, when adapting the lengths of the pipes and, for example, cutting a pipe in order to shorten it, part of the screw thread, or even all of it, is necessarily lost. So after cutting, another screw thread is difficult to produce in the field.
Moreover, the coupling device in the above application engages directly with screw threads provided on the ends of the pipes and made directly in the thickness of these pipes, thereby requiring the manufacture of pipes whose thickness is great enough to be able to incorporate the screw thread. This added thickness is useful only at the ends of the pipes bearing the screw threads, but is present over the entire length of the pipe since the end screw threads are formed only after the entire body of the pipes has been manufactured. It is therefore necessary to provide additional material for the manufacture of such pipes, which significantly increases the raw-material cost and the final weight of the pipe.
It is an object of the invention to provide a coupling device for composite pipes which is easy to assemble both in the factory and in the field and which does not increase the manufacturing cost of the composite pipes and consequently the cost of an installation, while still ensuring satisfactory strength and sealing of the pipes in the coupling zone.
According to the invention, the above and other objects are addressed by a device for coupling two pipes made of composite material based on a reinforced thermoplastic. The device comprises a sleeve intended to be joined, on one side, to an end of the first pipe and, on the other side, to an end of the second pipe, the sleeve being provided on its internal wall with at least one screw thread. A sealing element creates a seal in the coupling zone, and comprises a first end-piece intended to be fastened to the end of the first pipe and a second end-piece intended to be fastened to the end of the second pipe, each end-piece having over at least part of its external surface a screw thread intended to engage in a complementary manner with the screw thread of the sleeve.
The use of separate threaded end-pieces thus avoids increasing the thickness of the external jacket of the pipe over its entire length.
The two pipes may consist of a thermoplastic matrix, a layer of reinforced material coating the matrix, and a thermoplastic jacket covering the coating layer. At least the internal surface of the end-pieces is made of the same thermoplastic as that of the jacket of the pipes.
This identical material advantageously makes it possible to attach the end-pieces, after they have been heated, around the ends of the two pipes, these ends also being heated, in order to weld them together, after which they are cooled to consolidate them.
This way of fastening the end-pieces by welding, may thus be carried out both in the factory and in the field, something which is advantageous when the length of a pipe must be adapted in the field by cutting it. The end-pieces are adapted and easily attached in the field.
Advantageously, the length of the end-pieces is between 0.5 and 2 times the diameter of the pipes which are of cylindrical shape.
Preferably, the coating layer of the pipes and the external layer of the sleeve are based on a raw material consisting of comingled glass filaments and thermoplastic filaments, the thickness of the external layer of the sleeve being at least equal to that of the coating layer of the pipes.
According to another characteristic, the sleeve has on its internal wall two screw threads formed with opposite hands and located on either side of a mid-plane transverse to the longitudinal axis of the body of the sleeve, the two screw threads being intended to engage with the respective screw threads of the two end-pieces, the hand of the screw threads being matched to the hand of each screw thread of the sleeve. Moreover, indicia are provided on the end-pieces and on the sleeve for identifying the hand of the screw thread.
Advantageously, the screw thread or threads of the sleeve are formed of the same material as that of the screw threads of the end-pieces.
According to another characteristic, the sleeve includes, at its mid-plane, a groove intended to accommodate the sealing element against which the ends of the pipes provided with the end-pieces are intended to be pressed. Advantageously, the sealing element is sufficiently flexible to intimately follow the shape of the free cross sections of the ends of the pipes.